Drug-eluting implantable medical devices have become popular in recent times for their ability to perform their primary function such as structural support and their ability to medically treat the area in which they are implanted. For example, drug-eluting stents have been used to prevent restenosis in coronary arteries. Drug-eluting stents may administer therapeutic agents such as anti-inflammatory compounds that block local invasion/activation of monocytes, thus preventing the secretion of growth factors that may trigger VSMC proliferation and migration. Other potentially anti-restenotic compounds include antiproliferative agents, such as chemotherapeutics, which include sirolimus and paclitaxel. Other classes of drugs such as anti-thrombotics, anti-oxidants, platelet aggregation inhibitors and cytostatic agents have also been suggested for anti-restenotic use.
Drug-eluting medical devices may be coated with a polymeric material which, in turn, is impregnated with a drug or a combination of drugs. Once the medical device is implanted at a target location, the drug(s) is released from the polymer for treatment of the local tissues. The drug(s) is released by a process of diffusion through the polymer layer for biostable polymers, and/or as the polymer material degrades for biodegradable polymers.
Controlling the rate of elution of a drug from the drug impregnated polymeric material is generally based on the properties of the polymer material. However, at the conclusion of the elution process, the remaining polymer material in some instances has been linked to an adverse reaction with the vessel, possibly causing a small but dangerous clot to form. Further, drug impregnated polymer coatings on exposed surfaces of medical devices may flake off or otherwise be damaged during delivery, thereby preventing the drug from reaching the target site. Still further, drug impregnated polymer coatings are limited in the quantity of the drug to be delivered by the amount of a drug that the polymer coating can carry and the size of the medical device. Controlling the rate of elution using polymer coatings is also difficult.
Accordingly, drug-eluting medical devices that enable increased quantities of a drug to be delivered by the medical device, and allow for improved control of the elution rate of the drug, and improved methods of forming such medical devices are needed. Co-pending U.S. application Ser. No. 12/500,359, filed Jul. 9, 2009, U.S. Provisional Application No. 61/244,049, filed Sep. 20, 2009, U.S. Provisional Application No. 61/244,050, filed Sep. 20, 2009, and co-pending U.S. application Ser. No. 12/884,343, each incorporated by reference herein in their entirety, disclose methods for forming drug-eluting stents with hollow struts. In some applications, such as coronary stents, the diameter of the hollow strut lumen to be filled with the drug or therapeutic substance is extremely small, e.g. about 0.0015 in., which may make filling the lumen difficult. As such apparatus for and methods of loading a drug within a lumen of a hollow strut of a stent are needed.